1. Field of the Invention
The present invention relates to a pressure sensor for sensing pressure, and more particularly, to a capacitive pressure sensor for sensing pressure by using electrostatic capacitance.
2. Description of the Related Art
A capacitive pressure sensor is formed by bonding a substrate having a pressure-sensitive diaphragm, which is a movable electrode, and a substrate having a fixed electrode with a gap (cavity) between the pressure-sensitive diaphragm and the fixed electrode. When pressure is applied to the pressure-sensitive diaphragm, the pressure-sensitive diaphragm is deformed and the gap between the pressure-sensitive diaphragm and the fixed electrode is varied. Electrostatic capacitance between the pressure-sensitive diaphragm and the fixed electrode varies with the variation of the gap. Accordingly, a variation in pressure is sensed by using the variation of the electrostatic capacitance.
For example, in the capacitive pressure sensor, as shown in FIG. 5, a glass substrate 102 having a fixed electrode 103 is disposed on a supporting substrate 101. A silicon substrate 104 having a diaphragm 104a is bonded to the glass substrate 102. In such a capacitive pressure sensor, since an extraction electrode 105 for the fixed electrode 103, and an extraction electrode 106 for the movable electrode (diaphragm 104a) are patterned on the glass substrate 102, the extraction electrodes are disposed in a bonded area between the glass substrate 102 and the silicon substrate 104. An example of such a capacitive pressure sensor is disclosed in
However, in such a structure, the extraction electrodes 105 and 106 exist in the bonded area between the glass substrate 102 and the silicon substrate 104. Accordingly, in the extraction electrode 105 and 106, when the glass substrate 102 and the silicon substrate 104 are not properly bonded to each other, the cavity between the glass substrate 102 and the silicon substrate 104 is not sufficiently airtight. As a result, the diaphragm 104a does not serve as the movable electrode and the sensor dies not operate properly. When the glass substrate 102 and the silicon substrate 104 are not properly bonded to each other in the extraction electrodes 105 and 106, a contact resistance becomes unstable and a Q value of the sensor is not uniform.